Two satellites have seen “tsunami” spreading on the surface of the Sun after a release of matter into space called a coronal mass ejection (CME).
These tsunami of heightened magnetic field and hot, ionised gas race across the Sun at about 400km per second…
And thanks to data from Hinode, one of the two satellites, researchers may have cracked a 70-year-old mystery as to why the Sun’s surrounding corona is so much hotter than its surface.
The Japanese satellite Hinode has been studying the Sun since 2006, joined in Earth orbit by the Solar Dynamics Observatory in 2010.
Both satellites look at ultraviolet light from the Sun – colours we cannot see but that give hints as to both the chemical makeup and the extreme physical conditions at and near the Sun’s roiling, turbulent surface.
David Long of University College London and colleagues finally spotted what are known as EIT waves after a CME. Like a tsunami emanating from the point of a seismic event, EIT waves are shock waves that carry magnetic fields and hot, ionised “plasma”…
The SDO satellite was able to capture the ultraviolet light emitted as the wave spread out. From that, the team was able to determine the wave’s speed – some 400km per second – and its rough temperature, over a million degrees.
Meanwhile the Hinode satellite returned a high-resolution map of the density of the Sun’s surface every 45 seconds.
Using both data sets, the team was able to determine the strength of the magnetic field in the “quiet corona” – a tricky measurement of the Sun in its typical, quiescent state…
The temperature at the Sun’s core is some 15,000,000C, but its surface is below 6,000C. Yet the corona is known to be at a temperature in excess of 1,000,000C.
How the energy gets into the corona to keep up these temperatures has baffled astronomers for more than half a century.
One idea was that waves of magnetic energy rise from below the Sun’s surface, depositing energy into the corona higher up. But what remained unclear was whether the energy was lost on its journey.
Hinode observations of the polar coronal hole have allowed the pair to peek into this interim height and determine how the energy is coupled up from the surface into the corona.
In a preprint on the Arxiv server they show that enough energy is carried by these waves to keep the corona at its searing temperatures.
The energies, temperatures, processes in play in solar dynamics is beyond my science amateur’s easy understanding. But, I get to see how this has been acquired and analyzed – and it begins to fill in one more blank on our knowledge of the solar system and the star at its center. Bravo!